# Question about FMCW range-velocity plot

I am working on plotting range-velocity heatmap of the receiving FMCW signal. I actually have already plotted. However, I do not really understand the mapping relationship between Doppler FFT bin and velocity. I learned to map from 1d FFT bin to range with the following codes as the x-axis.

x = (0:ADCsample-1) - ADCsample/2;